Forgot all about those valves. But if they were messed up, wouldn’t it cough and spit more? And skip some combustion’s? Because it doesn’t seem to be doing that at all…Very smooth, just not at a fixed RPM. (while the throttle is fully open)
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I’m not exactly a 2 stroke guy, but with it at full throttle and it’s surging like that, it could either mean clogged jets or it has an internal governor that it’s surging against.
I would take the carburetor off and give it a good cleaning. Get some carb cleaning dip in a 4L can if you can find them. That’s what I do with small engine carbs, leave it in the dip overnight and it’s usually cleaned up enough.
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Have already removed and disassembled the carb as much as possible, didn’t fix it.
An internal governor… Like an internal throttle somehow? Inside the engine block? Or adjusting the timing in some odd way?
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This might describe it:
"I just realized…this is an old lawn boy, with a 2 storke engine. If the air-fuel ratio is a bit rich, it will sputter, then suddenly run like a banshee, then sputter again. Sometimes it will jump from one to another rather quickly, sometimes not. Will always sputter until it warms up. I think you need to turn the mixture screw in a little. "
https://www.doityourself.com/forum/outdoor-gasoline-electric-powered-equipment-small-engines/167086-old-old-lawn-boy-governor-problem.html
Are all old lawnboys 2-cycle? I have one I picked up. But it looked like a 4-stroke with an all aluminum deck, and I think points and condenser.
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Not every Lawnboy was 2 stroke, some used a Tecumseh vertical shaft engine.
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Will play with the mixture screw some more, but before, it didn’t seem to have any effect. Talking to someone else, I might have found an issue. The tube with the jets above it, had a tiny pinhole, to let fuel into that area. It used to be clogged. Now it seems clean again. But it remains a tiny pinhole. And I’ve tryed running this engine, with a fixed open throttle set-up. It might try to starve itself of fuel, due to the fuel not getting to the jets quick enough. Compared to the image I’m about to link: my hole could barely fit a 0.8 mm piece of welding wire. I’m considering drilling it out. (the engine might have ran just fine, if it wasn’t an open throttle situation)
Before I bought this particular lawnmower, I did do some research. More modern (but still very old) lawn boy engines, were 4-stroke. From what I’ve found, lawnmowers from the early 80’s and before that, used to be mainly 2-stroke for this particular brand. Think they started buying 4-strokes in the 90’s from tecumsen or whatever they are called. (a youtuber mentioned this in one of his vids)
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If it’s a push mower engine it should be running at full tilt anyways. I wouldn’t drill anything out.
2 strokes can be very cold natured and maybe let it warm up on choke for at least a minute before trying to open the throttle all the way.
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I’ve included a vid, and the vid does show a push mower. (although it does have rear wheel drive when being pushed)
I’ve had it run for 5 minutes. When I would use the choke, it would surge less and have a much lower speed. Often close to dying. Opening up the choke again, would get my max rpm for a second or two. I recorded this vid just after those 5-ish minutes, so it should have been warm by then.
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Poop, forgot to share a picture of a scimilar hole I was considering drilling out.
That same hole leading to the jets, is needle-sized on my carb. While it should be submerged in fuel anyways. So I’m kinda thinking: maybe it sucks up all the fuel, and the fuel doesn’t get replaced fast enough?
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It sounds like an air fuel mixture problem, I couldn’t tell from the video but did you have the air filter on the carburetor?
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Tryed with and without. Without it would rev up slightly higher. In this vid, it’s running without airfilter.
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Jahee, I am thinking that the governor on this one should be an external air vane. Operates only off of the flywheel blown air.
Follow the linkage back up under the top cover to verify this.
If so remove the top cover to inspect the air vane. Air vane pivot. Air/vane pull spring and for an opposing dampener spring.
Missing or weak pull spring could do this.
Missing or stretched dampener spring could do this.
Try and NET search up for pictures to the governor parts.
S.U.
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Not the same due to it being plastic, but it has indeed this air vane. It’s only removable if you take the carb off entirely. I can’t even figure out if the spring used to be a dampener spring or pull spring. It’s that messed up/weak/stretched. That’s also why I was using a rope to keep the throttle fully open.
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Yes I see.
The spring and air fin are built directly onto the throttle plate shaft. Hmm.
I did also fine this info link, since your carburetor picture ID’s this as a Duraforce?
http://www.mylawnmowerforum.com/threads/lawnboy-duraforce-surging-fix.21578/
If this is truly a 1988 era made, then the original carburetor was probably set up to be super lean for least smoke and emissions.
Too lean.
Good luck. I have confidence you will sort it out.
Steve Unruh
I had been looking for the cost of a replacement carb. This isn’t identical to the one I have, but has an near identical fin setup. Will check your link, and play some more with the carb. Maybe see if I can somehow fit a different carb. However, for now: time to get some sleep.
Outriggers. Just saying. Also you don’t have to sever a limb. Less than a two inch deep cut will sever your femoral Artery. I’d ride the damned thing though.
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Are you sure the float is set to the proper height?
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I wouldn’t drill it. I would put a straw on the can of carb cleaner and see if you can blow anything through. To me, it seems like the carb adjustment screw should either flood it or starve, and if that isn’t working then maybe it isn’t supplying enough for idle.
The next thing I would check is take the muffler off and look for carbon build-up on the exhaust, and scoring on the cylinders. In the link I posted, they mentioned those can have carbon build up, and you need to chip it away with the cylinder UP so it doesn’t fall into the engine, and careful not to hit the piston and do damage.
The other thing they were mentioning which I wasn’t quite following, was that it has like a second gear so when you hit tall grass it kicks the engine on harder for power but it also has a protection to keep it from revving at high speed with no load to prevent damage to the engine.
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I lied. It is actually an old snapper with an aluminum deck. I think early 70s like the v210…
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I know it wasn’t allowing in much if any fuel in before. After trimming a pin from the float, it can open up and allow fuel in. (float wasn’t able to drop enough) The float is made from plastic, and I don’t see any way to otherwise adjust it. Will check again.